448 Significance Sexually transmitted diseases (STDs), especially HIV, can result in death. But while not deadly, most STDs are responsible for significant neonatal morbidity, infertility and associated costs to society. Currently, with the exception of the Hepatitis B vaccine, there are no vaccines available to prevent sexually transmitted diseases. A better understanding of the factors which control immune responses in the genital tract may make it possible to develop such vaccines. There is ample evidence that the normal hormonal cycles of women affect the genital tract immune system. Objectives In this study, we sought to determine if exogenous estrogen could increase the genital and systemic immune response to a viral antigen. Results Six animals were immunized intramuscularly with an SIV antigen, p55. Three animals received 500 ug of estradiol at the time of immunization. This was repeated 3 times at 6 week intervals. During a 6 month observation period the number of antibody-secreting cell and the antibody titers in both group of animals were similar. Future Directions Studies are continuing in order to determine if there is a subtle effect on genital immunity that was not detected in the systemically. KEY WORDS steroid hormones, female genital immunity FUNDING NIH Grant HD29125